The present invention broadly relates to an electroplating bath and process for electrodepositing zinc as well as alloys of zinc on a conductive substrate, and more particularly, to an electroplating bath and process incorporating controlled effective amounts of a bath soluble and compatible AB-type polyamide brightening agent for enhancing the characteristics of the zinc or zinc alloy electrodeposit.
Zinc and zinc alloy electroplating baths of various types have heretofore been used or proposed for use for depositing a metal plating of a decorative or functional type on a variety of conductive substrates such as iron and steel, for example, to provide for improved corrosion resistance, enhance the decorative appearance and/or to build up the surface of a worn part enabling refinishing thereof to restore its original operating dimensions. Typically, zinc as well as alloys of zinc and nickel, zinc and cobalt and zinc, nickel and cobalt can provide decorative surface finishes of a semi-bright to a lustrous appearance while simultaneously enhancing the resistance of the substrate to corrosion. Such electroplating baths in addition to plating baths for depositing a zinc and iron alloy, a zinc, iron and nickel alloy as well as a zinc, cobalt and iron alloy have found widespread commercial use for industrial or functional plating applications including strip plating, conduit plating, wire plating, rod plating, tube plating, coupling plating, and the like. Zinc electroplating baths can also be satisfactorily applied in processes such as electrowinning and zinc electrorefining while zinc alloys containing iron in the alloy deposit are suitable for electroforming of worn parts, for plating of soldering iron tips and for plating of Intaglio plates for printing and the like.
A problem associated with prior art zinc and zinc alloy electroplating baths has been the inability to employ a brightening agent which could be satisfactorily employed in all types of such zinc and zinc alloy electroplating baths. Additionally, such brightening additives have generally been limited to use over relatively narrow current density ranges and the electrodeposition of a zinc or zinc alloy plate of high ductility has been difficult to obtain when using any one brigthening additive.
In the prior copending United States patent applications, a brightening additive is disclosed which overcomes many of the problems and disadvantages associated with prior art brightening agents for zinc and zinc alloy plating in that the brightening additive can be used in a wide variety of types of zinc and zinc alloy plating over a broad pH and current density range to achieve a zinc or zinc alloy electrodeposit of the desired brightness and required ductility characteristics thereby providing for improved flexibility and versatility in the use of the bath and process. The present invention is similarly directed to an improved brigthening agent or mixtures of brightening agents which can be effectively employed in zinc and zinc alloy plating baths providing improved flexibility and versatility in the use and control thereof and in the electrodeposition of zinc and zinc alloy electrodeposits possessed of the desired appearance and physical properties.